Conditional inclusion of a key-value pair in a hash [closed]

问题

Can someone help me shorten the following method? I began with this, which I liked just fine:

def self.some_hash
  { "foo" => "bar" }
end

Now I want to add an optional key. The tersest syntax I can think of is this:

def self.some_hash(some_key=nil)
  answer = { "foo" => "bar" }
  answer[some_key] = "yucky, long-winded syntax" if some_key
  answer
end

The modified method works, but I'm dissatisfied with waste of virtual ink. Is there a way to shorten it? I realize one could employ a ternary operator on the hash literal, but that would force (I think) the repetition the "foo" => "bar" pair on each branch of the condition, which is also slightly less than pristine.

回答1:

def self.some_hash(some_key = nil)
  {"foo" => "bar"}.merge(some_key ? {some_key => "yucky, long-winded syntax"} : {})
end

Or, if modifying the original hash,

def self.some_hash(some_key = nil)
  {"foo" => "bar"}
  .tap{|h| h.merge!(some_key => "yucky, long-winded syntax") if some_key}
end

Or, maybe you can do it in a way close to your original:

def self.some_hash(some_key = nil)
  {"foo" => "bar"}
  .tap{|h| h[some_key] = "yucky, long-winded syntax" if some_key}
end

回答2:

I don't really like it but this is pretty terse (and confusing)

def self.some_hash(some_key=nil)
  Hash[[["foo", "bar"], [some_key, "some value"]].select(&:first)]
end

This may be a little better.

def self.some_hash(some_key=nil)
  {"foo" => "bar", some_key => "some_value"}.keep_if{ |k, _| k }
end

Hash#keep_if

来源：https://stackoverflow.com/questions/14175958/conditional-inclusion-of-a-key-value-pair-in-a-hash

标签

ruby

hashtable